The present application relates to an optical member for use in a liquid crystal display or the like, and a display device.
As a thin-type display device, a liquid crystal display (LCD) is used. In a liquid crystal display, a backlight for illuminating the entire plane of a liquid crystal panel from the back is used. Depending on the structure of the backlight, liquid crystal displays are roughly divided into the direct light type and the edge light type. The edge light type uses a light guide plate in which a light emitting element is disposed for a side face. Light entering from the side face of the light guide plate is allowed to propagate in the light guide plate and is extracted from the top face of the light guide plate. On the other hand, the direct light type performs plane emission by, for example, disposing a plurality of fluorescent tube lamps such as CCFLs (Cold Cathode Fluorescent Lamps) on a substrate (see, for example, Japanese Unexamined Patent Application Publication No. 2005-108635 (patent document 1)).
In recent years, as a liquid crystal display is becoming larger, thinner, lighter, and longer lasting, from the viewpoint of improvement in motion picture characteristics by blinking control, attention is being paid to a light emitting device performing plane emission by disposing a plurality of light emitting diodes (LEDs) on a substrate. In such a light emitting device, to extract white color, the following two methods are mainly used. In the first method, light emitting diodes for emitting light of three colors of R, G, and B are disposed and turned on simultaneously, thereby synthesizing the light of the three colors. In the second method, for example, a blue light emitting diode chip is surrounded by a phosphor layer which performs color conversion. By mixing color light obtained by the conversion in the phosphor layer and blue light. which passed through the phosphor layer without being converted, white light is obtained.
Recently, attention is being paid to, as a third method, a method of performing plane emission by disposing a plurality of blue light emitting diode chips on a substrate and providing a sheet-shaped phosphor layer (phosphor sheet) on the blue light emitting diode chips.
The phosphor as described above is generally weak to oxygen and moisture vapor and, when it is exposed to oxygen, moisture vapor, or the like, the phosphor deteriorates. Accordingly, the color conversion efficiency of the phosphor decreases, and luminance and chromaticity of the backlight deteriorates. Such deterioration in the phosphor is conspicuous particularly under high-temperature high-moisture environments.
To address the deterioration, a method of improving moisture vapor transmittance and gas permeability of a phosphor sheet itself (see Japanese Examined Patent Application Publication No. H06-58440 (patent document 2)) and a method of applying an application liquid for protection onto the surface of a phosphor sheet (see Japanese Unexamined Patent Application Publication No. S59-42500 (patent document 3)) are proposed. A method of sandwiching a phosphor sheet by two glass plates and sealing the phosphor sheet is also proposed (see Japanese Unexamined Patent Application Publication No. 2007-23267 (patent document 4)). Such a phosphor sheet is used by being stacked together with a diffusion plate, a diffusion film, a lens film, and the like between a liquid crystal panel and a light source of a blue light emitting diode or the like